* <p>Null nodes are strictly forbidden.
 *
 * <p>Because this is an abstract class, not an interface, you can't use a lambda expression to
 * implement it:
 *
 * {@snippet :
 * // won't work
 * TreeTraverser<NodeType> traverser = node -> node.getChildNodes();
 * }
 *
 * Instead, you can pass a lambda expression to the {@code using} factory method:
 *
 * {@snippet :

   * that pass this regex are valid -- only a performance hit is incurred, not a semantics bug.
   */
  @GwtIncompatible // regular expressions
  static final
  java.util.regex.Pattern
      FLOATING_POINT_PATTERN = fpPattern();

  @GwtIncompatible // regular expressions
  private static
  java.util.regex.Pattern
      fpPattern() {
    /*

     * @param regex The regular expression for the client.
     * @param client The CrawlerClient instance.
     */
    @Override
    public void addClient(final String regex, final CrawlerClient client) {
        factory.addClient(regex, client);
    }

    /**
     * Adds a client to the wrapped factory at a specific position.
     * @param regex The regular expression for the client.

 * resulting {@link HashCode} is dependent only on the bytes inserted, and the order in which they
 * were inserted, not how those bytes were chunked into discrete put() operations. For example, the
 * following three expressions all generate colliding hash codes:
 *
 * {@snippet :
 * newHasher().putByte(b1).putByte(b2).putByte(b3).hash()
 * newHasher().putByte(b1).putBytes(new byte[] { b2, b3 }).hash()

Create functions with a name that starts with `test_` (this is standard `pytest` conventions).

Use the `TestClient` object the same way as you do with `httpx`.

Write simple `assert` statements with the standard Python expressions that you need to check (again, standard `pytest`).

{* ../../docs_src/app_testing/tutorial001.py hl[2,12,15:18] *}

/// tip

Notice that the testing functions are normal `def`, not `async def`.

 * appropriate primitive specialization such as {@code IntSupplier}) instead whenever possible.
 * Otherwise, at least reduce <i>explicit</i> dependencies on this type by using lambda expressions
 * or method references instead of classes, leaving your code easier to migrate in the future.
 *
 * <p>To use an existing supplier instance (say, named {@code supplier}) in a context where the

## Ajouter des validations par expressions régulières

On peut définir une <abbr title="Une expression régulière, regex ou regexp est une suite de caractères qui définit un pattern de correspondance pour les chaînes de caractères.">expression régulière</abbr> à laquelle le paramètre doit correspondre :

{* ../../docs_src/query_params_str_validations/tutorial004.py hl[10] *}

    }

    /**
     * Retrieves a list of XPath nodes from the document.
     *
     * @param doc The XML document.
     * @param xpath The XPath expression.
     * @return A list of XPath nodes.
     * @throws XPathExpressionException if an XPath expression error occurs.
     */
    protected XPathNodes getNodeList(final Document doc, final String xpath) throws XPathExpressionException {

    /** Map of parser properties. */
    protected Map<String, String> propertyMap = new HashMap<>();

    /** XPath expression for extracting content from the document body. */
    protected String contentXpath = "//BODY";

    /** Map of metadata field names to their corresponding XPath expressions. */
    protected Map<String, String> metadataXpathMap = new HashMap<>();

    /** HTTP header name for robots tag */
    private static final String X_ROBOTS_TAG = "X-Robots-Tag";

    /** XPath expression for extracting thumbnail content from meta tags */
    private static final String META_NAME_THUMBNAIL_CONTENT = "//META[@name=\"thumbnail\" or @name=\"THUMBNAIL\"]/@content";

    /** XPath expression for extracting Open Graph image content from meta tags */